What we think of as new has probably been done before if you take time to search for it. Google patents is the easiest way to search the USPTO content. We use patents as a time stamped proof of design activity which is of course traceable and a legal document.
Some Excavator History
Scotsman James Watt and Englishman Matthew Boulton developed the first steam powered excavator all the way back in 1796. No excavator patent seems to have been applied for but these two were partners in the steam engine business. As I am sure you know many books have been written about these gentlemen. We know the agricultural revolution and the industrial revolution drove the replacement of animal and human power in large scale agricultural work as well as mass excavation construction projects for the expanding canal network and later on the railway network.
William Smith Otis was related to the Otis family who created elevators. Unfortunately he died soon after his patent for the first steam powered excavator at the very young age of 26.
This steam powered excavator from 1897 starts to look like an excavator of today. You can see a rack and pinion being used for the slew mechanism in place of the hydraulic (or sometimes electric) motor driven reduction gearbox pinion gear and slew ring gear used today and the boom and arm (a.k.a. dipper or stick) are recognisable. The machine did not use cables but steam cylinders as actuators so it is fluid powered but not truly hydraulically powered. The word hydraulic is from the ancient Greek words "huder" (water) & "aulos" (pipe) so it generally refers to liquid power. The steam being compressible would have probably meant control issues for the bucket path.
Some Mini-excavator History
We know Mini-excavators are basically smaller versions of regular excavators. The Mini-excavator has now become the most popular type of construction machine in the world by volume.
Definitions change between manufacturers but Mini-excavators generally run from 1 ton up to 6 tons. Micro-excavators fit below them, and Midi-excavators fit above them. There are lots of versions and options, and many different manufacturers around the world.
The Smalley 360 mini-excavator is recognised as the first Mini-excavator from 1959 even though it does not have a dedicated transmission (see below). This Smalley machine was exported in volume to Japan in the late 1960's timeframe so it may have been the inspiration for other excavator manufacturers to build on the idea of shrinking the excavator for smaller building sites rather than mass excavation sites.
The next evolutionary step is when Yanmar created the YNB300 Mini-excavator in 1968, it was a wheeled machine with a transmission and a rigid chassis rather than the upper structure and undercarriage we know today.
Then the Takeuchi TB300 was created around 1970 and the TB1000 around 1971. The TB1000 had a separate upper structure and a tracked undercarriage and full 360 degree slewing (as well as kingpost offset swing) so all the ingredients of the mini-excavator were now in place in this model from 1971.
Richard Smalley is recognised as the inventor of the mini-excavator in 1959. The Smalley 360 mini-excavator did not have the transmission and track arrangement we know today but it did have a slew mechanism and a mini excavator hoe arm. The machine used the hoe to pull itself around the building site. Mr. Smalley has many other machine designs in his portfolio of creations.
In this Hitachi Construction Equipment patent you can clearly see the form of a modern Mini Excavator with the upper structure and the lower under-carriage incorporating the track drive motors. The patent is actually for an amphibious machine but the public domain patent allows the use of the illustration from the correct time period of 1972. This shows that a number of Japanese manufacturers had clearly embraced the mini excavator concept and were working on advancing the designs.
